eval does work at macro expansion time, but only where it is actually possible to evaluate the expression its given with only the information available at macro expansion time at hand.
One case where there is not enough information -- and a minimal "Can't eval locals" example -- is the following: (defmacro foo [x] (eval x)) (let [y 1] (foo y)) Are you doing something similar...? eval's behaviour here is very sensible, since it is asked to eval the Symbol y at compile time, when it knows that it names a local binding, but does not know what the value of that local binding is going to be at runtime. (It could conceivably notice that this particular local is given a constant initializer expression, but that would only raise expectations for cases like (let [y (some-function)] (foo y)) where using the compile-time return value of (some-function) would make no sense even if it were possible to obtain it.) That doesn't mean eval'ing stuff at compile time is not possible, it's just that one has to make sure that one is eval'ing forms which have meaningful compile-time values. Sincerely, Michał PS. Actually it's fun to go code diving to see how this breaks exactly... Although it's not terribly helpful in writing code. A summary of the code path this goes through is, I think, that clojure.core/eval delegates to clojure.lang.Compiler.eval, which in turn needs the expression analysed by clojure.lang.Compiler.analyze, which in this case delegates to clojure.lang.Compiler.analyzeSymbol, which in this case -- called at compile-time inside this particular let form -- finds a binding for the Symbol y included in the local environment and accordingly returns a LocalBindingExpr, which is something un-eval-able. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
